Larger vehicles need increased braking capacity and that translates into increasing the size of vacuum boosters. Larger vacuum boosters require larger power pistons. The increase in the size of the power piston relates to an increase in both the diameter and length of the power piston. This creates a significant challenge for the designers of the vacuum booster power piston.
The power piston is the most critical part of the vacuum booster and as such performs numerous functions such as transmitting input load, transmitting load from the primary and secondary diaphragms/support plates, receiving and maintaining a floating control valve, and determining the reaction ratio. These functions dictate that the power piston must sustain high levels of stress and exhibit tight tolerances to achieve the desired performance requirements. In larger and longer stroke vacuum booster applications, it is now extremely difficult to obtain a power piston that can handle the combination of high loading conditions and tight tolerances due to the capability and quality problems associated with the molding of a longer power piston. To overcome this problem, brake manufactures are starting to make power pistons in two pieces.
However, two-piece power piston arrangements presented additional challenges to brake manufactures. The assembly of a tandem power piston is cumbersome because of the multitude of parts to be assembled and alignment problem between the primary power piston the secondary power piston during assembly. Additionally, there have been problems in effectively connecting the two-piece power piston. There has also been a problem with establishing and maintaining an airtight seal between the two pieces of the tandem power piston, the primary piston and secondary piston.
It would be desirable, therefore, to provide a vehicle braking system vacuum booster tandem power piston connection design that overcomes these and other disadvantages.